Design And Test Of Aluminum Matrix Composites Synergy Reinforced By Micron-SiC And Nano-TiC Particle

Piston is the vital part of an engine and its operating conditions are extremely harsh.Thus,the piston materials should have the outstanding performance.In order to improve the mechanical property of Al-Si piston alloy,we strengthened the alloy by changing the size of the second-phase(Primary-Si,Eutectic-Si,CuNi-rich)and adding the micron-SiC and nano-TiC particle to the matrix.The effects of the second-phase and reinforcements on the stress-strain field and yield strength in alloy were acquired.In the process,the microstructure of Al-Si piston alloy was obtained by a series of continuous optical metallography(OM),and then built the 3D reconstruction subjected to the OM.The distribution and microstructure of the second phase in the alloy were studied.The interface and microstructure of composites was characterized by means of SEM and TEM.The mechanical property was examined by tensile test and nano-indentation test.3D modelings of the second-phase and the reinforcements were established,and the representative volume element(RVE)modelings based on the 3D modelings were built.The influence of second-phase size,particle content and particle size,interface bonding on the performance of alloy was investigated by finite element method(FEM),the results were given a experimental verification.All research shows that :(1)3D reconstruction shows that the morphology of primary-Si is an polyhedral bulk,but the eutectic-Si is long strip-like,the statistical results show that the total volume of all the silicon phase is 12.59%.And most of the primary-Si in the piston alloy is connected with the eutectic-Si.However,the space structure of the intermetallic compounds is a complex netstructure.The intermetallic compound has a relatively independent distribution due to they have no connection with each other.Its total volume is 3.43%.The spatial structure of the Fe-rich phase is an irregular block with less content in the alloy where they isolate in it.(2)The corner of the primary-Si is easy to cause the stress concentration.But with the primary silicon size becomes smaller,the stress of the corners decreases while the strength increases.On the other hand,the matrix plasticity is poorer.Eutectic-Si is the main contributor to the strength of the alloy.With the decrease of the size,the strength of the alloy rises up sharply,but the plasticity is smaller.The relatively high elastic modulus of CuNi-rich phase makes it plays a major role in the alloy system,and the mesh like structure is also beneficial to the strengthening of the alloy.With the decrease of the size,the contribution to the performance of the alloy is larger.However,their mechanical strengthening is not obvious on the yield strength because of the low content.(3)The nano-TiC particles have a fine-grain strengthening effect on matrix in the TiCp/Al composites.And the Hall-Petch formula was used to quantify the strengthening so as to embed the amount in the property of matrix in the finite element method.The effects of the size and content of TiC on the properties of composites were studied.The results shows that the enhancement effect of TiC on 200 nm is significantly higher than that of 500 nm.With the increase of the content,they all play an important role in strengthening the matrix.The difference between 5wt.% content of TiCp/Al composites yield strength and the 3wt.% is small,but the high content of particles will have a worse effect on the plasticity of the matrix.In the case of 1wt.% and 3wt.% of 500 nm particles reinforcement matrix,the experimental values and the predicted values of yield strength are in good agreement.(4)The interfacial bonding between particles and matrix in SiC_p/Al composites has a great influence on the properties of composites.However the interface debonding and damage happened by the loading.When the interfacial strength is greater than 500 MPa,the performance of the composites has a lower increase.But when it is less than that of 200 MPa,and the mechanical properties of composites decrease sharply.The experiment curve matches the predicted 200 MPa interface strength curve.The content of Si C is greater than 1wt.%,which has an effective strengthening function.With the increase of the particle content,the yield strength of the composites increases while the plasticity decreases.